1. Field of the Invention:
This invention relates to printed circuit boards and more particularly, to such boards having plated through-holes. Still more particularly, this invention relates to the preparation of printed circuit boards with plated through-holes using self supporting photohardenable sheets in an additive plating process.
2. Description of the Prior Art:
Printed circuits can be prepared by depositing copper conductor patterns directly on insulating substrates by processes such as those disclosed in U.S. Pat. Nos. 3,060,024; 3,146,125; 3,259,559; 3,347,724; 3,391,455; 3,506,482; 3,628,999 and 3,791,858. In preparing printed circuits with plated through-holes using electrodes plating, cleaning procedures are frequently needed after activation of holes and circuit lines in order to remove unwanted catalyst from non-circuit areas before electroless plating. Besides the cost of the cleaning procedures, expensive catalyst is wasted in the non-circuit areas. Printed circuits with plated through-holes ae also prepared by electroless plating using substrate layers having dispersed catalytic particles therein. In these instances however, additional masking layers are needed to produce the desired circuit patterns.
Photosensitive and particularly photohardenable layers are conventionally used to prepare printed circuit boards. The use of such layers is disclosed in U.S. Pat. Nos. 3,469,982; 3,526,504; 3,622,334; 3,778,270; 3,837,860 and French Pat. No. 7211658. Also self supported photohardenable sheets have been disclosed in U.S. Pat. Nos. 3,865,589; 3,210,187; 3,259,499, as well as Belgian Pat. No. 596,378 and British Pat. No. 618,181. These imaged, photohardenable and photosensitive sheets are processed by removing unhardened material from the sheet to produce a mask image. Also, no provision is made to introduce plated through-holes by the processes disclosed.